Test points generated by HDI board proofing
In a mass production factory, you cannot use an electric meter to slowly measure whether each resistance, capacitance, inductance, or even each HDI board is correct. Therefore, the so-called ICT(In-Circuit Testing) has appeared. Automatic testing machine, which uses multiple probes (usually called "nail bed" fixtures) to simultaneously touch all the parts on the board that need to be measured, the characteristics of these electronic parts are then programmed to measure the parts sequentially in a sequential primary and side-by-side method. Generally, depending on the number of parts on the circuit board, it only takes 1-2 minutes to test all the parts on the general board., The more parts, the longer the time.
However, if these probes directly contact the electronic components or their solder feet on the HDI board proofing, they may crush some electronic components, but it will be counterproductive, so there will be a test point, and the two ends of the probe will draw a pair of circle parts. There is no solder resist on the small shaped points, so the test probe can touch these small points without directly contacting the electronic part to be measured.
In the early days when there was a traditional plug-in (DIP) on the HDI board proofing, the solder feet of the parts were indeed used as test points, because the solder feet of the traditional parts were strong enough to not be afraid of needle punching, but there were often The probe misjudged poor contact, because after general electronic parts are processed by wave soldering or SMT tin, a residual flux residual film is usually formed on the solder surface, and the resistance of the film is very high, which usually leads to poor contact of the probe. Therefore, at that time, we often saw the test operators on the production line, who often took the spray gun and blew desperately, or wiped the wine in these places where testing was needed.
However, with the development of technology, the size of HDI board proofing is getting smaller and smaller. It is already a bit difficult to squeeze so many electronic parts on a small circuit board. Thus, the problem of test points occupying board space is often a tug of war between the design side and the manufacturing side. The appearance of the test point is usually round, because the probe is also round, so it is easier to produce, and it is easier to bring adjacent probes close, so that the needle density of the needle bed can be increased.
Proofing of HDI board
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